Alloy Electric
Can any one help me with this?
The S-N behavior of a brass alloy shaft is shown below. The shaft is used to make a coupling that is attached to an electric motor operating at 365 rpm.
What is the maximum torsional stress (in MPa) that can be applied to the shaft if the coupling must operate for 12 days?
Use decimal notation, digits after decimal: 0
The link for the Graph:
http://cg-love.com/s1/79armu1.jpg
365 Rev/min * 60min/hr * 24hr/day *12days = 6.3 million revs. Since this is fully reversed alternating loading, there are 2 cycles/rev, therefore 12.6 million loading cycles. Since your chart only goes up to 8 (assuming million), I guess this thought was neglected, so your best bet is to go with 6.3 @ 200MPa.
But there are special calculations for fatigue of a reversed alternating load, and I'm not going to quote my failure mechanics book to you, so figure it out if you need to be more precise.
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